This invention relates to an intravascular catheter useful for extracorporeal blood circulation through an artificial kidney, an artificial lung, or the like.
In a conventional blood dialyzing operation using an artificial kidney, a couple of needles are kept inserted respectively to each of the vein and artery of a patient for the suction and recovery of blood through the artificial kidney. In this case, the patient is obliged to suffer from a great deal of pain because two needles are stuck to his blood vessels. In addition, the life of the shunt serving to connect directly the artery and the vein tends to be shortened.
To overcome the above-noted drawbacks, a so-called "single needle system" has been proposed in which withdrawing from and returning to the body of the blood are effected by using a single needle. In this case, the opening-closing of a valve is performed electrically so as to enable the single needle to withdraw and return the blood alternately. The alternate operation naturally leads to a longer dialyzing time than for the case of using two needles, because shortening of the dialyzing time, will cause sharp and enlarged fluctuation in the internal pressure of the dialyzing circuit, giving bad influences to the patient. It should also be noted that the single needle system necessitates a particular machine for operating the circulation.
U.S. Pat. No. 4,073,297 discloses an extracorporeal blood circulation method utilizing a single-walled catheter or a double-walled catheter. In the U.S. Patent, the forward end portion of the catheter is provided with a plurality of bores extending the wall thereof and suitably apart from each other. In determining the locations of the bores, however, attentions are paid to only the mechanical strength of the catheter. In addition, one of the bores is located at the top portion of the wall when the catheter is horizontally disposed such that the tapered surface of the needle included in the catheter is faced vertically upward. It has been found, however, that the bore thus located gives rise to detrimental effects in operation of the catheter.